Tennis ball and spray. High-speed photograph of spray produced as a wet tennis ball with backspin travels through the air. The rapidly rotating ball produces a centrifugal force that pushes water to the equator of the ball and then flings it outwards as a radial spray.

Tennis ball Splashed:

Tennis ball and splash. High-speed photograph of the splash produced as a tennis ball bounces off a wet surface. As the ball impacts the ground, it deforms and displaces a ring of water, which rises up in the shape of a crown, or corona.

It is especially fascinating because the red color of the water drop helps you visualize the intricate hydrodynamics of the falling drop with the water surface.

You see the real struggle the red drop is going through to stay away from the water. I see three bounces here, each creating its daughter droplet, which in turn bounces back.

So what happens? When a drop encounters a solid surface, its initial spherical shape is forced into a pancake-like form that stretches out over the surface. The kinetic energy of the drop forces it to conform to the planar geometry of the solid surface.

If the liquid in the drop is attracted to the surface, it will continue to spread and eventually adhere to the so-called hydrophilic material. The extent of the spreading is determined by the molecular interactions between the drop and the liquid.

When the molecular interactions between the water drop and the surface are repulsive, water droplets landing on these surfaces try to minimize their contact with the surface.

Thus, after being forced into a pancake shape, the drops retract as they try to re-establish a spherical form to minimize their exposure to the surface. Indeed, for certain cases the retraction can be sufficiently violent that the drop actually rebounds or bounces off the surface after impact

Here you see several attempts by the drop to return to its spherical shape.

This full-scale Schlieren image shows the discharge of a .44 Magnum revolver.

The basic optical Schlieren system uses light from a single collimated source shining on a target object. Variations in refractive index caused by density gradients in the fluid distort the collimated light beam. This distortion creates a spatial variation in the intensity of the light, which can be visualized directly with a system designed to capture shadows.

Two spherical shock waves are seen, one centered about the gun’s muzzle (the muzzle blast) and a second centered on the cylinder.

Penn State Gas Dynamics Lab seems to have generated this image. Normally I would link to the lab, but it hasn’t been updated in a while. However, You can see some spectacular Schlieren image images taken by Gary Settles of Penn State in the NY Times article: Mysterious Cough, caught on film. Talk Like a Physicist